The present invention relates to a light emitting diode device using a light emitting diode (LED), for illuminating a display such as a liquid crystal display.
FIG. 8 is a sectional view showing a conventional LED device of a fluorescence color mixing type for emitting white color light.
The LED device 10 comprises a substrate 1 having a pair of terminal electrodes 2, 3 provided on the upper surface and the underside thereof, and a blue LED 4 emitting blue light. The LED 4 and the upper surface of the substrate 1 are covered by a transparent resin 5. In the resin 5, phosphor particles 6 of YAG are mixed. The LED device 10 emits white light Pw by color mixing as described hereinafter.
Referring to FIG. 9 which is an enlarged view of a part of FIG. 8, when a driving voltage is applied to the terminal electrodes 2 and 3, the LED 4 is excited to emit blue light Pb. When the blue light Pb meets the particle 6, the blue light Pb changes into yellow light Py based on the wavelength conversion. The yellow light Py is mixed with the blue light Pb which has not met the particle 6, so that the mixture of the yellow light and blue light takes on white. Thus, the LED device produces the white light Pw.
FIG. 10 is a wavelength characteristic graph of the LED device 10. A luminous intensity curve H1 has a peak Kb at wavelength 450 μm of the blue light component, and has a peak Ky at wavelength 550 μm of yellow light component. However, there is no peak at wavelength 650 μm of the red light component. Since the red light component is hardly included, the emitted white light tones cold blue light.
FIG. 11 is a wavelength characteristic graph of the LED device and an RGB color filter which is used in a color display. When blue or green is selected by the filter, display of each color is obtained. However, when red is selected, red light is scarcely included in a passing range of the red light filter. Consequently, a red selected part tones red yellow color.
Therefore, if the LED device is used for illuminating the display, a red selecting part is displayed with red yellow color.